Reflectivity of metallodielectric photonic glasses

We report on the fabrication and optical properties of metallodielectric photonic glasses of colloidal silver spheres with a radius ranging from 200 to 420 nm and volume fractions around 60%. Strong modulations (~25%) in the optical reflectivity were observed in the visible range for these structures, despite the presence of only short-range order. Despite the strong wavelength dependence of silver dielectric constant, the spectral positions of the optical reflection peaks, with the exception of the smallest size (200 nm), scale linearly with the particle radius. For the smallest particle size studied, a peak at longer wavelengths related to a lower order gap was observed. Remarkably, the general features in the reflectivity spectra have a qualitative similarity to spectra calculated for light incident on (111) oriented face-centered-cubic (fcc) crystals.